A fiber optic coupler is used in optical fiber interconnection arrangements to couple electromagnetic waves from one of two or more optical fibers to another optical fiber in the group. Alternatively, the coupler may couple one optical fiber to itself to form a loop. Such couplers have been used in optical communications, optical sensors, and fiber optic gyroscopes. A fiber optic coupler is formed by fusing and tapering two or more optical fibers together. The fabrication usually involves aligning principle axes of two or more optical fibers after removing a portion of a protective jacket on the optical fibers. They are then brought together and heated to fuse and taper the optical fibers resulting in a fused and tapered coupled region for coupling of optical power.
Fiber optic couplers are very sensitive to environmental influences because the optical material of which the optical fibers are made is very fragile. In addition, the coupling region is not provided with the jacket so adverse environments influence the quality of the optical material of the fiber optic coupler and/or the signals transmitted through the fiber optic coupler. Therefore, the optical signal processing performance of a fiber optic coupler in various environments typically depends upon the type of housing or package in which it is positioned for protection and on the method used to assemble the packaged fiber optic coupler.
In a fused fiber optic coupler, the fused and tapered portions of the coupler where the transfer of optical power takes place is structurally weak and sensitive to environmental conditions. The extinction ratio and the transmissibility of the coupler can be degraded if the materials used in the package for the fiber optic coupler subject the fiber optic coupler to a non-uniform distribution of stresses, either during the fabrication process, or thereafter during use due to changes in environmental conditions.
Packaging techniques which have been used to protect the fiber optic coupler from deleterious environmental influences include the use of quartz glass tubes as protective covering and as a support for the coupled region of a fiber optic coupler. In such an arrangement, the coupled region is typically placed within a central open portion of a slotted quartz glass tube and epoxy is applied at the ends of the tube to secure the optical fibers extending therefrom and the coupled region to the tube. However, difficulties arise in environments in which substantial shock or vibration occur because of the resulting material movements of the coupled region of the fiber optic coupler suspended in the central open portion of the tube.
In part, the above difficulties have been overcome by placing the fibers within the slotted glass tube and then heating the mid-region of the tube until it collapses about the fiber by stretching the tube to reduce the diameter thereof. This method places the tube in direct contact with the optical fibers and the coupled region of the fiber optic coupler, thereby providing rigid support to the coupled region. However, this places additional stress on the coupled region causing losses and other difficulties.
With a fiber optic coupler secured in a slotted glass tube with epoxy applied at both ends of the tubes to hold the coupler in tension, degradation in processing performance of the fiber optic coupler occurs in deleterious environmental conditions. This degradation occurs because the epoxy holding the fiber optic coupler in tension is partly placed on a jacketed lead portion extending from ends of the slotted tube and, in addition, partly positioned to secure the bare optical fibers between the jacketed portion and the coupled region to the glass tube. Application of the adhesive to the bare optical fibers is necessary because if the adhesive is only placed to secure the jacketed lead portions to the glass tube, the unstripped or jacketed fiber allows slippage underneath the jacket. Such adhesive on the base filters causes degradation in processing performance.
Techniques such as those discussed above for packaging fiber optic couplers leave much to be desired for protecting the coupler. This protection is especially lacking where the fiber optic coupler and the packaging thereof are often subjected to extremely high or extremely low temperatures, to very high temperature variations in relatively short periods of time, and/or to vibrations or impacts of controlled magnitudes. Thus, it has been observed that the failure or breakage rate of fiber optic couplers encased in such manners, presents a severe limitation to the use of such packaged fiber optic couplers in communication applications. Therefore, an improved package and packaging method for fiber optic couplers is desired.